Topic 9: Seperate Chemistry 2 Flashcards
What is the test for sulfates?
- Add dilute hydrochloric acid (to remove any carbonate ions that might obscure results) and barium chloride solution to a solution
- If sulfate ions are present, a white precipitate of barium sulfate will form
What is the test for chloride?
- Add nitric acid and silver nitrate solution to a solution
- If chloride ions are present, a white precipitate will form of silver chloride
What is the test for bromide?
- Add nitric acid and silver nitrate solution to a solution
- If bromide ions are present, a cream precipitate will form of silver bromide
What is the test for iodide?
- Add nitric acid and silver nitrate solution to a solution
- If iodide ions are present, a yellow precipitate will form of silver iodide
What are the 3 halides you need to know tests for?
- Chloride
- Bromide
- Iodide
What is the test for carbonates?
- Add a couple of drops of a dilute acid to a solution which will fizz if carbonate ions are present
- Connect the test tube with the solution to a test tube with limewater
- If carbonate ions are present, the limewater will turn milky as carbon dioxide will be formed (and limewater turns cloudy/milky when carbon dioxide is present)
What is the test for metal cations?
- Add a few drops of sodium hydroxide to a solution
- The colour of the precipitate that forms depends on the metal ion in the solution
When testing for metal cations using sodium hydroxide, what colour is the precipitate formed if calcium is present in the solution?
White
When testing for metal cations using sodium hydroxide, what colour is the precipitate formed if copper (II) is present in the solution?
Blue
When testing for metal cations using sodium hydroxide, what colour is the precipitate formed if iron (II) is present in the solution?
Green
When testing for metal cations using sodium hydroxide, what colour is the precipitate formed if iron (III) is present in the solution?
Brown
When testing for metal cations using sodium hydroxide, what colour is the precipitate formed if aluminium is present in the solution?
White
BUT with excess NaOH, the precipitate re-dissolves to form a colourless solution
What is the test of ammonium ions?
- Add sodium hydroxide solution to the solution you’re testing and gently heat
- If ammonium ions are present, ammonia gas will be given off
- Ammonia gas turns damp red litmus paper blue - so that how you can check if ammonium ions are present
What colour does a flame turn in a flame test if calcium ions are present in the sample?
Orange-red flame
What colour does a flame turn in a flame test if sodium ions are present in the sample?
Yellow flame
What colour does a flame turn in a flame test if potassium ions are present in the sample?
Lilac flame
What colour does a flame turn in a flame test if lithium ions are present in the sample?
Crimson flame
What colour does a flame turn in a flame test if copper ions are present in the sample?
Blue-green flame
Disadvantages of flame tests?
If the sample contains a mixture of metal ions, the flame colours of some ions may be hidden by the colours of other - may not give you the correct results
What is instrumental analysis?
Tests that use machines
3 advantages of instrumental analysis?
- Sensitive - can detect even the tiniest amounts of ions
- Fast - tests can be automated
- Accurate - don’t involve human error
What are 2 uses of flame photometry?
- Identifying ions in solution
- Determining the concentration of ions
How does flame photometry identify ions in a solution?
Each ions produces a unique line spectrum - allows you to compare with a reference spectra
How can flame photometry determine the concentration of ions?
The intensity of the lines on the spectrum can allow this to be calculated:
1. Find the intensity that’s been measured on the graph
2. Correspond this to the concentration using the calibration curve (line on the graph)
What is flame photometry an example of?
Instrumental analysis
If multiple ions are present in the sample in flame photometry, what happens to the spectrum?
The spectrum will be a combination of all of the ions’s individual spectra
What are alkanes?
The simplest type of hydrocarbons, containing only single covalent bonds
What is the general formula for alkanes?
CnH2n+2
Are alkanes saturated or unsaturated? Why?
They’re saturated - all the atoms have formed single covalent bonds with as many other atoms as possible
What are the first 4 alkanes in the alkane homologous series? WITH FORMULAS
Methane CH4
Ethane C2H6
Propane C3H8
Butane C4H10
How to remember the order of the first 4 compounds in all hydrocarbon homologous series?
Monkeys
Eat
Pink
Bananas
What is an alkene?
Hydrocarbons that have one C=C double bond functional group
What is a functional group?
A group of atoms in a molecule that dictate how that molecule typically reacts
Are alkenes saturated or unsaturated? Why?
Unsaturated - the double bind can open up to form other bonds
What are the first 3 alkenes in the alkene homologous series? WITH FORMULAS
Ethene C2H4
Propene C3H6
Butene C4H8
NO METHENE BECAUSE AN ALKENE NEEDS TO HAVE AT LEAST 2 CARBONS TO HAVE A CARBON DOUBLE BOND AND METHENE WOULD ONLY HAVE 1 CARBON MOLECULE
What can happen to the double bond in alkenes in addition reactions?
It opens up - another substance adds across the double C=C bond
What is the test for alkenes?
- Add solution to bromine water
- Shake the mixture
- If the mixture turns colourless, alkene is present
If an alkane is added to bromine water, what happens?
Nothing - the bromine water remains orange (doesn’t turn colourless like it does for alkenes)
What is the equation for combustion of hydrocarbons?
Hydrocarbon + oxygen —> carbon dioxide + water
What are polymers?
Substances made by joining lots of small repeating units (monomers), they have a high average Mr
What is addition polymerisation?
When molecules with C=C bonds join together in addition reactions
Describe the process of addition polymerisation?
- A monomer (e.g. ethene) will open up its carbon double bond
- This will then allow the same monomers to join up to each other and form a polymer (e.g. poly(ethene))
What are polymers named after?
The monomers that they’re formed from
Describe the steps of drawing the displayed formula of a polymer from its monomer
- Draw the alkene carbons and replace the double bond with a single bond
- Add an extra single bond to each carbon atom
- Add the other groups in the same way that they surround where the double bond was
- Add brackets and an ‘n’ at the bottom